feat(Input): Added secure input functionality for typing passwords

[CatchABus]

This PR adds secure functionality for inputs that accept passwords.
It will replace all characters with * and secure state is toggleable itself.

Input will accept secure as an option and instance property.

Now, let's say develop wants to add a show/hide password button like most forms do nowadays.
By setting property secure to false, Input will display the original text content. Setting it back to true will display asterisks again.

Additionally, I took the chance to improve performance on character deletion a little bit by using substring instead of array operations.